The invention relates to a device for measuring the filling level of a fuel tank, in particular for motor vehicles. Specifically, the inventive device has two openings for installation of a filling connection and a pump unit.
The known devices for measuring the filling level of a fuel tank, in particular for motor vehicles, operate with a float which is arranged on the free end of a pivotably mounted lever or in an immersion tube. The height of the float can be determined by using electric contacts, for example, which are arranged in the path of movement of the flow and/or the lever. The float closes an electric circuit, the length of which changes with the height of the float. The height of the float and thus the filling level of the fuel tank are defined by the resistance of the circuit. These known sensor systems are installed as individual modules by means of a flange or on fuel pumps in the tank. Because of the size of the lever tank sensor and the path described by the float, an ideal arrangement of the lever tank sensor in the tank and its mounting are difficult to implement for reasons of space. Furthermore, the insertion of the lever tank sensor into the tank is complicated because of the compact design of the sensor. Since the lever tank sensor is mounted on the pump unit, a compromise must be made with regard to positioning. The immersion tube sensor is subject to the disadvantage that for reasons of space, its flange cannot be situated in the upper area of the tank. Therefore, the filling level of the tank above the flange of the immersion tube sensor cannot be determined. The lever tank sensor and the immersion tube sensor both have the disadvantage that their mechanism of operation is based on the movement of a float and a particular installation opening must be provided in the tank.
An object of the present invention is to create a generic measurement device which does not have any moving parts, is largely independent of the dimensional shape of the fuel tank and does not necessitate any additional installation opening.
A measurement device corresponding to these requirements is characterized according to this invention in that a film sensor is provided with an electric connecting cable which can be connected through the pump unit to a display device and the film sensor is embedded in a protective tube which is provided with inlet openings for the fuel, and the protective tube is mounted on the filling connection at the side and can be inserted jointly with it into the respective opening in the fuel tank.
The film sensor used as part of this invention is known per se. It is a film having an electric heating device arranged on the back side and a plurality of thermocouples, which are part of an electric circuit, arranged on the front side. When the thermocouples are heated by the electric heating device, they generate a voltage. Since the thermal conductivity of a liquid is much higher than that of air, the thermocouples immersed in the liquid will heat up less than the thermocouples surrounded by air. With a certain heating power of the electric heating device, the filling level of the liquid can therefore be deduced from the voltage generated by the totality of thermocouples.
With the inventive measurement device, the protective tube serves not only to protect the film sensor from mechanical damage but also imparts the measurement arrangement adequate rigidity so that the lower end of the film sensor can be arranged at the lowest point in the fuel tank. The protective tube is inserted jointly with the filling connection into the respective opening in the fuel tank, and the connecting cable is passed out of the fuel tank and through the pump unit. The inventive measurement device therefore does not necessitate any additional openings. Due to the fact that the protective tube is mounted on the filling connection at the side, there is no risk of it colliding with the gun nozzle during the process of filling the tank.
In an expedient embodiment of the invention, the connecting cable is connected by a plug connection to one or more electric lines embedded in the pump unit. After joint insertion of the filling connection and the protective tube together with the film sensor in the tank, the connecting cable can be led out of the tank at the side through the opening provided for the fuel pump and connected to the pump unit which is then inserted into the tank opening.
In the case of a split fuel tank such as that conventionally used with motorcycles, joint installation of the filling connection and the protective tube may pose problems. In this case, the upper end of the protective tube is connected in an articulated joint to the filling connection. This may be accomplished, for example, by the fact that the upper end of the protective tube is provided with a hook which is hung in a harness attached to the side of the filling connection.
If the position of the lower end of the protective tube is not defined by the dimensional shape of the fuel tank, it may be expedient to provide the lower end of the protective tube with fastening means for fastening same to the bottom of the fuel tank. To this end, a spring clamp may be provided at the lower end of the protective tube so that the spring clamp can be engaged in a non-positive manner with an engagement area provided on the bottom of the fuel tank.
The protective tube is preferably comprised of two half-shells which are locked together, forming a slot. Fuel can penetrate through the slot into the interior of the protective tube so that fuel flows around the film sensor up to the filling level of the tank.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.